The present invention relates to a weaving method and an apparatus for producing a fabric with variable width.
JP 7-238433 discloses a woven tube whose diameter is changed along the length in that weft threads of different elasticities are inserted in the warp direction.
Fabrics can be produced both as a two-dimensional, one-layered sheet and in the form of multi-layered, thicker structures. Woven tubes with diameters variable along their lengths could up to now not be produced without seams because the known methods for changing the width of the fabric are not applicable in this case.
One possibility for changing the width of the fabric resides in the concentration and spreading of the warp threads. In doing so, the overall number of the warp threads in the fabric remains constant. Of course, the width of the fabric and thus possibly also the diameter of a woven hollow space is changed in the process; however, the spreading and also the contraction of the lateral distance between the warp threads are resisted by the warp thread tension, the weft insertion and the weft thread tension, which is inevitable and for other reasons even desired. The spreading and thus the contraction are thus not stable and will essentially be lost during the weaving. Therefore, a desired change of width cannot be easily performed.
It is an object of the invention to provide a weaving method and a weaving apparatus which is able to produce a stable fabric of threads, especially weft threads, of uniform elasticity and stretchability and with a width that can be varied along the length of the fabric, particularly a tube-shaped fabric whose diameter varies along the length, and in such a manner that very considerable changes of width can be performed per length unit. The change of diameter is to be effected not by the elasticity and stretchability of the threads but by the weaving method itself.
The above and other objects and advantages of the invention are achieved by the provision of a weaving method and apparatus wherein the reed is displaced so as to change the warp thread spacing and thus the width of the advancing fabric in accordance with a predetermined program which represents a desired fabric width which varies along the length of the sheet of warp threads. At least the two opposite edges of the formed interwoven fabric are engaged with spreader devices which impart a width guiding effect to the engaged opposite edges. Also, the width guiding effect is adjusted as a function of the desired fabric width.
The invention offers the advantage that the spreading of the fabric, which is per se known and usual, is utilized actively here for adapting the lateral warp thread position and the weft-thread deposit and tension to the width of the fabric. This makes it possible to obtain strong conical enlargements or reductions of the fabric width which will be permanently applied to the fabric structure and be rigidified therein.
The terms xe2x80x9cspreadersxe2x80x9d or xe2x80x9cspreader devicesxe2x80x9d are used herein to designate known devices which exert a spreading effect on the fabric.
Particularly preferred are spreaders which are used only on the edges of the fabric. Such spreaders are e.g. needle-equipped circular cylindrical rollers arranged for free rotation in the region of the edge of the fabric. The edge of the fabric is guided via these rollers while partially wound around them. The end faces of the rollers are preferably arranged in parallel to each other but inclined to a radial plane of the rollers. This results in an outward conveying effect. According to the invention, these rollers, with respect to the fabric width, are displaced toward the outside or the inside synchronously and substantially proportionately to the spreading or contraction of the warp thread distance.
Further known are spreaders in the form of non-rotating or rotating rods extending across the width of the fabric. These are e.g. rods wherein the circumference contacting the fabric is provided with grooves facing toward the outside in the direction of the production of the fabric.
When producing fabrics with varying width, the closest contraction depends on the largest possible warp thread density. When spreading such a warp thread sheet, the problem occurs that the warp threads will not become distributed in a uniform manner across the spread fabric width. This problem is solved by the weaving method wherein two or more immediately adjacent warp threads are guided without mutual tying as is the case e.g. with a longitudinal filling rep with 4 warp ascents and 4 warp descents. Such a tying offers the advantage that the friction between the warp threads and the weft threads is low so that the warp threads also after the weft insertion can be distributed across the fabric width due to their inherent tension.
A special form of the fabric is the circular or tube fabric. A tube is woven e.g. in that two fabric layers are produced to lie above each other, being connected only in the edge regions.
In prior methods for weaving tube-like structures, a constant fabric width is generated. The diameter of the woven hollow space, mostly a woven tube, will thus be constant. In many applications, however, a hollow-space-forming fabric is desired which has a more or less tapering diameter or a constant conicity between two different diameters or widths. Examples thereof are fiber reinforcements for poles (sail or surf masts, supporting buttresses) which in the upper region have a small diameter and down to the base have a gradually increasing diameter. Other examples are golf clubs and many light construction rods and supporting arms in industry.
Conically tapering structures with hollow spaces can up to now be produced only by the winding method or the braiding method. The winding method is very time-consuming and is restricted by the danger that threads on the winding core might slide off. The winding method is not suited to place threads in the circumferential direction of a tube and thus is confined to torsion-stressed applications.
The disclosed embodiments of the invention have the object to produce a woven structure which forms a hollow space, e.g. in the manner of a tube, and whose threads extend in the axial and circumferential directions, and whose hollow space increases or decreases in the direction of the warp threads.
In one embodiment, the shuttle weaving technology is of advantage since, in this case, the weft thread, while being uncut, will alternately tie the upper and the lower fabric layers so that a seam region will not be generated on the circumference of the woven tube.
When use is made of narrow fabric needle loom automats, the weft thread on one end of the fabric has to be attached by a crochet edge which will cause a more or less distinct protrusion in the warp direction.
Also the use of modern high-performance rapier weaving machines is made possible by the simultaneous production of a plurality of bands or tubes with variable width or variable diameter. This machine also permits the production of a tube shaped fabric with two longitudinal seams, and the material-saving production of a plurality of bands or tubes with variable width/variable diameter. Through an embodiment wherein the edge region of the fabric layers is connected by a crocket edge, the seam region of the tube is reinforced so that the tube can also be subjected to high pressures inside.
An embodiment of the invention makes it possible to produce bands or tubes which, while having a variable width on the one hand and resp. a variable diameter on the other hand, are also curved along their length. For this purpose, use can be made e.g. of conical take-off rollers. Of particular advantage, however, is the use of take-off rollers separated into segments, wherein each segment conveys one or a group of warp threads and wherein the individual segments can be driven at a controllable speed which is different from segment to segment. In this regard, reference is made to DE Patent 39 15 085.
An embodiment of the invention makes it possible that the number of warp threads per width unit is compensated for by removal of warp threads through measures from binding technology and resp. inclusion of warp threads into the binding.
Individual warp threads or groups of warp threads can temporarily remain in the upper shed or lower shed position while the other warp threads are woven or tied up. Thus, these threads will temporarily float. In such places where these threads are again tied into the fabric, there is generated a tendency of an enlargement of the fabric width and resp. of the width of the woven hollow space or of the tube diameter. Advantageously, use is made of a jacquard machine with individual thread control.
Very steep changes of the fabric width are made possible by the weaving method wherein the weft tension is controllable. The increase of the weft thread tension leads to a contraction of the warp threads and also to a changed fabric width. Of advantage in this regard is a controllable weft thread brake which will break the weft thread to a higher extent at certain points of time and to a lower extent at other points of time.
The spreading or contraction of the warp thread distance is advantageously performed by a reed with variable dent spacing. In this case, the reed dents can be arranged for lateral movement on the reed frame. The lateral displacement can provide the required space for the warp threads in a passive manner, i.e. without further drive means. However, use can be made also of an active displacement through a drive means which will laterally guide and position the reed dents.
Alternatively, a fan weaving reed with non-parallel reed dents wherein the reed dents diverge in the manner of a fan in the vertical direction and which can be adjusted in height. Both embodiments of reeds are described and illustrated e.g. in DE 39 15 085 A1.
The configuration of the reed dents disclosed herein is useful for the reduction of thread friction and thread damage in case of a massive spreading or contraction of the warp thread distance.
When using a reed with laterally adjustable reed dents or a vertically adjustable weaving reed with non-parallel, i.e. fan-like reed dents, it is to be considered that, in the area of the largest contraction, it is not possible to accommodate as many reed dents across the smallest fabric width as required for guiding the warp threads. Thus, between two reed dents, a number of warp threads must be inserted which is too large for a proper guidance. In the height region with enlarged distance, i.e. large thread spreading, a sufficient lateral guidance is lacking so that the uniform distribution of threads will become problematic then.
To solve this problem, additional guiding rods are arranged between reed dents. The warp threads, while being distributed in a uniform manner, are pulled both into the interspaces (main openings) between the main reed dents and into the interspaces (additional openings) between the additional reed dents. In the region of the contraction, the guiding rods are neutral, i.e. they do not guide the warp threads upon beat-up. In the region of the spreading, however, they enter the main openings and serve for the substantially uniform distribution of the warp threads accommodated there.
The additional guide dents can be arranged on the reed or be provided as the reed dents of a further reed (additional reed). It is also possible to provide these two reeds in an identical configuration and to cause the additional reed to be slightly offset laterally, i.e. by less than one reed unit (opening width), in its upper position effecting the spreading.
The tube-shaped fabric woven from warp and weft threads according to the invention is configured to form, from two fabric layers arranged on each other, a hollow space which under the influence of an internal pressure takes on a substantially circular cross section, with the diameter varying along the length of the fabric tube. In this regard, it is accomplished according to the invention that the mutually overlying fabric layers are connected to each other so tightly that they will withstand also to high internal pressures, with the fabric layers on the edges merging without seams into each other by means of the endlessly inserted weft thread, forming a seamless hollow space with variable width or variable diameter, while the fabric layers in the region of the hollow space are not connected to each other.
For this purpose, the conventional shuttle weaving technology is of particular advantage. By this weaving technology, the whole weft bobbin is conveyed through the weaving shed and thus will form a so-called xe2x80x9ctruexe2x80x9d edge, i.e. the weft thread is not severed on the edge but is folded over and inserted into the following shed. In various bindings, e.g. the tabby hollow weave, use is made of this condition. In such cases, the weft thread is alternately inserted into an upper and a lower fabric layer. The completed fabric thus has a tube-like structure with seam regions since the upper layer on the edge will merge into the lower layer without interruption. When combining this manner of generating the hollow spaces with the proposed width variations, one will obtain a seamless woven tube with different diameters.
Tube-shaped fabrics and particularly such fabrics with variable diameters cannot be bent in the inflated condition and cannot be inflated in a bent condition. The method wherein the drawing off of the warp sheet is varied across the width of the fabric, makes it possible to produce such a fabric. This fabric is distinguished in that the distance of the binding points between the warp and weft threads increases from the one edge to the other edge of the two tube-forming fabric layers and preferably increases in a linear manner so that the fabric is bent in the longitudinal direction in a plane. Such a bent xe2x80x9chollowxe2x80x9d fabric is also advantageous as a tube having a constant width in the longitudinal direction and resp. of constant diameter when the tube is to be inflated. In this manner, the shape that the tube is to take in the inflated condition can be determined by weaving. If the curvature is not determined by weaving, the tube will develop folds and take on a random shape in the inflated condition.
It should be noted that also more than two layers can be woven above each other, e.g. three layers. This will result in two hollow spaces or chambers extending in the warp direction. Also then, the desired changes of the width will also cause a contraction or widening of the hollow spaces.